Conventionally, handheld computers, laptop computers, personal computers, and other mobile electronic devices may utilize dynamic random access memory (DRAM) devices. A dynamic random access memory is capable of retaining data for only a fraction of a second. Accordingly, data stored in DRAM is typically refreshed, that is read and then rewritten, at a rate somewhat faster than the data would naturally decay, often on the order of 4,000 to 8,000 times per second.
Conventional DRAM chips include special circuitry, known as self-refresh circuitry, that allows the DRAM device to perform the refresh operation automatically and without external circuitry. Such circuitry is used in a special self-refresh mode, when it is not necessary to provide the data to external logic such as a computer processor. It is well understood that a faster refresh rate consumes more power relative to a rate which is slower.
As DRAM devices are used in many handheld computers and other mobile electronic devices, engineers and designers of such mobile electronic devices are consistently concerned with the overall power budget of the device and attempts at lowering power requirements for the devices is of paramount importance. Conventional DRAM chips require that the operating voltage be at approximately 3.3 volts, to both retain data and enable the self-refresh operations. Further, it has been recognized that the rate at which data decays within a DRAM cell is directly related to the operating temperature. The higher the operating temperature, the faster the data decays. Typically, semiconductor devices, including DRAM devices are designed for operation in environments up to approximately 70 degrees C. However, in the case of handheld computers, most are designed for temperatures of up to about 55 degrees C. and typically operate in environments at about 30 degrees C. Accordingly, most conventional DRAM devices are designed to refresh at rates much higher than would be required considering the typical operating temperatures seen by the devices. Thus, extraneous power is being expended in carrying out the higher than necessary refresh rates.
Accordingly, there is a need for a memory device useable in mobile electronic devices in which power requirements are lessened as compared with conventional memory devices. Further, there is a need for a memory device useable in a mobile electronic device in which the refresh rate of the memory device may be adjusted according to operating temperature. Further still, there is a need for a memory device useable in a mobile electronic device in which the refresh rate is adjusted periodically according to a predicted temperature. Yet further still, there is a need for a method of adjusting the refresh rate of a memory device by estimating the future operating temperature.
The teachings herein below extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above mentioned needs.
An exemplary embodiment relates to a mobile electronic device. The mobile electronic device includes a housing and a processor supported by the housing. The mobile electronic device also includes a memory device coupled to the processor, the memory device including an adjustable self-refresh rate setting configured to determine the self-refresh rate of the memory device. The mobile electronic device further includes a temperature sensor supported by the housing, coupled to the processor and configured to measure a temperature. Further still, the mobile electronic device includes a computer program logic running on the processor, the computer program logic configured to predict a future temperature and change the adjustable self-refresh rate setting based on the predicted future temperature.
Another exemplary embodiment relates to a method of changing the self-refresh rate for a memory circuit having an adjustable refresh rate. The method includes defining a temperature compensated self-refresh rate (TCSR) value. The method also includes measuring a temperature associated with the temperature of the memory circuit. Further, the method includes providing a new TCSR value if the temperature is greater than the current TCSR value. Further still, the method includes storing the current temperature reading with at least one other previous temperature reading. Yet further still, the method includes calculating a predicted temperature reading based on the current temperature and the at least one other previous temperature reading and providing a new TCSR value if the predicted temperature is greater than the current TCSR value.
Yet another exemplary embodiment relates to a handheld computer. The handheld computer includes a housing, a display supported by the housing, a processor supported by the housing and coupled to the display. The handheld computer also includes low power synchronous dynamic random access memory (LPDRAM) coupled to the processor, the LPDRAM including a temperature compensated self-refresh rate (TCSR) setting configured to determine the self-refresh rate of the LPDRAM. The handheld computer also includes a temperature sensor supported by the housing, coupled to the processor and configured to measure a temperature. Further, the handheld computer includes computer program logic running on the processor, and configured to predict a future temperature and change the TCSR based on the predicted future temperature.